Who is Afraid of Centrifugal Force?

Abstract

opment of the theory of gravitation. Newton's early manuscripts reveal that he had considered the possibility that terrestrial gravity may extend as far as the moon and solar attraction to the planets already from the late 1660s. This was an important first step towards the theory of universal gravitation. Moreover, by combining the expression for the outward tendency, which following Huygens' 1673 Horologium oscillatorium became known as centrifugal force, and Kepler's harmonic or third law of planetary motion, Newton had envisaged that both terrestrial gravity and solar attraction would be inversely as the square of the distance, on the assumption that centrifugal force would follow a similar rule as gravity and solar attraction.82 Analogous views were later aired among the London mathematicians Christopher Wren, Edmond Halley, and Robert Hooke.83 In view of Newton's very early speculations, it seems hard to defend a substantive role for Hooke's in the development of Newton's views towards universal gravity. Therefore my main concern here is with Hooke's analysis of curvilinear motion, since this appears potentially to have been his chief contribution to the debate. As Hooke put it to Newton on 24 November 1679, after having asked for objections to his speculations: And particularly if you will let me know your thoughts of that of compounding the celestiall motions of the planetts of a direct motion by the tangent & an attractive motion towards the centrall body. 84